Power transmissions include a torque converter which is effective to transmit power from an engine to a multi-speed power transmission. The torque converter permits the transmission to operate at a neutral condition without disengaging the clutches and/or brakes in the transmission. The torque converter will also provide power to a power take-off gear (PTO). When significant PTO power or high engine power without vehicle travel is required, the transmission gearing is placed in neutral so that the engine can operate at elevated power levels.
In vehicles such as cement mixers, the throttle setting and therefore the engine speed and power requirement can be quite high during load mixing. Engine speeds in the range of 2000 to 3000 rpm are not uncommon during these operations. Since the hydraulic control pump is driven directly by the torque converter impeller, the pump speed, output volume and torque converter pressure are quite high. Under this condition, a significant amount of oil is circulated to the torque converter and the lubrication and cooling circuits causing an increase in the volume of oil sent to the lubrication and cooling circuit; and also to the bushing supporting the hub connecting the impeller with the control pump.
Under this condition, it has been found that an inordinate amount of oil can bypass a lip seal which sealingly abuts the control pump drive hub on the torque converter impeller. The area beyond the seal is open to atmosphere therefore, any leakage which occurs will be visible. It has been noted that this condition appears after many hours of operation and not in transmissions newly put into use.
One solution to the problem is found in U.S. patent application Ser. No. 09/149,126, filed Sep. 8, 1998, which is assigned to the assignee of this application.